1. Field of the Invention
The present invention relates to a lens coupled to an optical fiber, and particularly relates to an inclined surface-equipped lens having an inclined surface that is inclined relative to a plane perpendicular to an optical axis.
2. Description of the Related Art
In an optical communication module, a lens is used for coupling light from a light-emitting element to an optical fiber.
In such a case, it is known to reduce reflected return light from an end surface of the optical fiber to the light-emitting element. As a method for reducing the reflected return light, Japanese Unexamined Patent Application Publication No. 61-87112 discloses an optical communication module in which an obliquely-cut surface of an optical fiber and a lens whose surface facing the obliquely-cut surface of the optical fiber is partially or entirely inclined are abutted and fixed to each other by means of an adhesive or the like.
As a method for manufacturing such a lens having an inclined surface, it is known that a lens material is heated in a body mold and press-molded with a mold having an inclined surface. Japanese Patent No. 4214694 discloses an inclined surface-equipped cylindrical lens having an inclined surface that includes in its part a surface substantially parallel to a plane perpendicular to an optical axis, as a countermeasure against a crack or the like occurring during press molding.
As shown in FIG. 10, in an optical communication module 500 disclosed in Japanese Unexamined Patent Application Publication No. 61-87112, a cylindrical holder 504 retains a rod-shaped lens 501 and an optical fiber 502 at its center. An end face 501a of the rod-shaped lens 501 and an end face 503a of a cladding 503 including an end face of a core 502a of the optical fiber 502 are abutted and fixed to each other via an optical adhesive such that their optical axes 505 coincide with each other. In this case, a portion of the end face of the rod-shaped lens 501 is an inclined surface. In addition, a portion of the end face that is not the inclined surface is a surface 501b perpendicular to the optical axis 505. It should be noted that the rod-shaped lens 501 is used for introducing light into the core 502a of the optical fiber 502 or outputting light from the optical fiber 502.
As shown in FIG. 11, an inclined surface-equipped cylindrical lens 600 disclosed in Japanese Patent No. 4214694 is a lens having an inclined surface 601. Reference numeral 603 denotes a spherical surface or an aspherical surface, and reference numeral 604 denotes an optical axis corresponding to the central axis of the lens having the spherical surface or the aspherical surface. The inclined surface-equipped cylindrical lens 600 has the inclined surface 601 that includes in its part a surface 602 substantially parallel to a plane perpendicular to the optical axis 604.
Specifically, in Japanese Unexamined Patent Application Publication No. 61-87112 and Japanese Patent No. 4214694, as shown in FIG. 12, a portion of the lens end face is an inclined surface 700a, and another portion of the lens end face is a surface 700b substantially parallel to a plane perpendicular to the optical axis. For that, a lens material 705 is heated, and press-molded with a lower mold 702 that has a surface 702a inclined relative to an optical axis 706 and a surface 702b perpendicular to the optical axis 706, as shown in FIG. 13. At that time, the surface 702a inclined relative to the optical axis 706 applies a pressing pressure 702d to the lens material 705 in a direction perpendicular to the optical axis 706.
Thus, as shown in FIG. 13, the lens material 705 spews out to the gaps between a body mold 703 and molds 701 and 702 on the side (Y1 direction side) on which the pressing pressure 702d is applied in the direction perpendicular to the optical axis 706, thereby forming protrusions 700c. As a result, during cooling, due to contraction, the protrusions 700c fit into the gaps between the molds 701 and 702 and the body mold 703. Thus, the lens 700 may not be released from the mold. In addition, the protrusion 700c of the lens 700 may be chipped off during mold release or transport, and a crack may occur from the chipped portion.